A circuit breaker is a device that can be used to protect an electrical circuit from damage caused by an overload or a short circuit. If a power surge occurs in a circuit protected by the circuit breaker, for example, the breaker will trip. This will cause a breaker that is in the “on” position to flip to the “off” position, and will interrupt the electrical power leading from that breaker. By tripping in this way a circuit breaker can prevent a fire from starting on an overloaded circuit, and can also prevent damage to the device that is drawing the electricity or to other devices connected to the protected circuit.
A standard circuit breaker has an input and an output. Generally, the input receives incoming electricity, most often from a power company. This is sometimes be referred to as the “line” terminal of the circuit breaker. The output, sometimes referred to as the “load” terminal, feeds out of the circuit breaker and connects to the electrical components being fed from the circuit breaker. A circuit breaker may protect an individual component connected directly to the circuit breaker, for example, an air conditioner, or a circuit breaker may protect multiple components, for example, household appliances connected to a power circuit which terminates at electrical outlets.
A circuit breaker can be used as an alternative to a fuse. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. When the power to an area shuts down, an operator can inspect the electrical panel to see which breaker has tripped to the “off” position. The breaker can then be flipped to the “on” position and power will resume again.
In general, a circuit breaker has two contacts located inside of a housing which are used to make and break a connection between the line and the load. Typically, the first contact is stationary, and may be connected to either the line or the load. Typically, the second contact is movable with respect to the first contact, such that when the circuit breaker is in the “off,” or tripped position, a gap exists between the first and second contact, and the line is disconnected from the load.
In circuit breakers that operate by separating contacts, the energized contacts separate when the circuit breaker is tripped, causing a gap to widen between the contacts while the movable contact moves from the closed position to the open position.
As the contacts begin to separate from a closed position, or complete closure from an open position, a very small gap exists between the contacts for a brief time while the contacts are closed or opened. An electric arc may be generated across this gap if the voltage between the contacts is high enough. This is because the breakdown voltage between the contacts is positively related to distance under pressure and voltage conditions in typical applications.
The creation of an arc during switching or tripping the circuit breaker can result in undesirable side effects which can negatively affect the operation of the circuit breaker, and which can create a safety hazard.
These effects can have consequences for the operation of the circuit breaker.
One possible consequence is that the arc may short to other objects in the circuit breaker and/or to surrounding objects, causing damage and presenting a potential fire or electrocution safety hazard.
Another consequence of arcing is that the arc energy damages the contacts, causing some material to escape into the air as fine particulate matter. The debris which has been melted off of the contacts can migrate or be flung into the mechanism of the circuit breaker, destroying the mechanism or reducing its operational lifespan.
Another effect of arcing stems from the extremely high temperature of the arc (tens of thousands of degrees Celsius) which can crack the surrounding gas molecules creating ozone, carbon monoxide, and other compounds. The arc can also ionize the surrounding gasses, potentially creating alternate conduction paths.
What is desired therefore, is a circuit breaker having an arc shield which addresses these limitations.